how to handle ip addresses in NGINX as a "multi load balancer"

So, I am setting up a new server rack with lots of Apache web-servers, some of which are related to each other, and some which are totally independent of each other (different customers). I have both IPv4 and IPv6 addresses enough to give them all "real" addresses if I wanted to, but I am thinking of putting a host with NGINX at the edge as a "load balancer" (some customers have more than one apache server so it is a real load balancer, but for other customers we have one 1 apache server, but I want them behind an nginx for flexibility). so... there are many ways to do this I guess... and I was thinking since I have so many real ip-addresses I would use them.. but how?

I could give each apache web server a real ip address, but why? I could give nginx-load balancer all the ip addresses, and give each customer a real ip address at the load balancer (is that a good idea?) I could put the ip addresses at the firewall and then from there just make NAT rules to point at the load balancer (nginx)... or maybe there is something I did not think about?

or should I just use 1 ip address for them ALL, and use name in URL to separate them at the NGINX? please help with input here.